On a cross sectional surface X1 of a pump electrode 3 in a gas sensor element forming a gas sensor, a noble metal area 31 having Pt—Au aggregations, a solid electrolyte area 32 having solid electrolyte aggregations, a mixture area in which Pt—Au alloy and solid electrolyte are distributed, and pores 34. The mixture area 33 is formed within a range of 30 to 90% in an overall area of the cross sectional surface X1, excepting the pores 34. The pores are formed adjacent to the mixture area 33.